What Is a Small Stroke?

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If you have had a small stroke, you might hear that you had a subcortical stroke or a brainstem stroke or a small cortical stroke. A small stroke is often called a small vessel stroke or a white matter stroke. The meaning of a subcortical stroke is that it is a stroke of the deep subcortical region of the brain, in contrast to a cortical stroke, which affects the large outer layer of the brain, or the cerebral cortex.


A subcortical stroke is usually caused by a blockage or bleed of a small blood vessel in the brain. While a subcortical stroke is generally small in location, it can cause significant signs and symptoms.

Internal Capsule

The internal capsule, an area deep within the brain, sends messages back and forth between the higher functioning areas of the brain and the brain stem and spinal cord, particularly messages related to movement. The internal capsule controls movements on the opposite side of the body. A stroke in the subcortical area can cause mild weakness, severe weakness or complete paralysis of the opposite arm or leg or both. A stroke involving the subcortical part of the brain rarely affects thinking, judgment or language. A stroke affecting the internal capsule is usually caused by bleeding or blockage of a small branch of the right or left middle cerebral artery.


The thalamus, also deep within the brain, is a center for putting together sensory signals from the body and then sending them to higher areas of the cerebral cortex.

An injury of the thalamus interferes with that message. A thalamic stroke can cause numbness, tingling or even complete loss of sensation of the arm or leg or both. The right side of the thalamus transmits sensation from the left side of the body and the left side of the thalamus transmits sensation from the right side of the body.

A thalamic stroke the may result from interruption of blood flow or bleeding of a branch of the right or left middle cerebral artery.

Basal Ganglia

The basal ganglia, another subcortical region of the brain, controls sophisticated functions that require coordination and smooth muscle movements. A stroke affecting the basal ganglia can cause symptoms such as shaking, jerking, or Parkinson’s disease-like tremors.

White Matter

Subcortical areas are often referred to as white matter because the neurons appear to be whiter than the grey appearing areas of the brain. The white appearance is a result of myelin, a specialized type of fat that covers brain and nerve cells to protect and insulate them, allowing the electrical signals to travel quickly and efficiently. 

Blood Vessels

Arteries carry blood to the brain. When arteries are blocked or when the blood flow is interrupted, ischemia, or lack of blood supply occurs. The brain tissue that suffers from a ischemia undergoes a process called infarction, which is chemical damage that results from an ischemia. 

Small strokes are often called subcortical strokes or small vessel strokes or white matter strokes. They can be caused by a blood clot resulting from cerebrovascular disease or from an embolus (a traveling blood clot) elsewhere in the body.

Usually a subcortical stroke occurs because of blockage of a small branch of the middle cerebral artery, a small branch of the anterior cerebral artery or a small branch of the posterior cerebral artery. Sometimes a subcortical stroke is the result of a hemorrhage (bleeding blood vessel.) A hemorrhage can result from a ruptured blood vessel, bleeding of an infarct, called hemorrhagic transformation, or from cancer that spread to the brain. It is more common for a cortical stroke to transform into a hemorrhagic stroke than it is for a subcortical stroke to transform into a hemorrhagic stroke. Other serious complications, such as brain swelling and edema, are less common with subcortical strokes than with cortical strokes.


While the signs symptoms of a small stroke can be significant, they are usually not life threatening. With rehabilitation and risk factor management, maximal recovery and prevention of additional strokes can be achieved.

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